1. Field of the Invention
The present invention relates to a realistic robot having a structure which emulates the mechanisms and movements of an organism, and, more particularly, to a leg-movement-type robot having a structure which emulates the body mechanisms and movements of, for example, a human being or a monkey, which walks while it is in an erect posture.
Even more specifically, the present invention relates to a leg-movement-type robot which walks on two feet while it is in an erect posture and which includes what one calls the upper half of the body, including the trunk, the head, the arms, and the like, provided on the legs. Still more specifically, the present invention relates to a robot which can move naturally in a way close to that of a human being and in a way sufficiently indicative of emotions and feelings with considerable fewer degrees of freedom than the actual mechanism of, for example, the human body.
2. Description of the Related Art
A robot is a mechanical device which emulates the movement of a human being by making use of electrical and magnetic actions. The term robot is said to be derived from the Slavic word ROBOTA (slavish machine). In our country, the use of robots began from the end of the 1960s, most of which were industrial robots, such as manipulators and conveyance robots, used, for example, for the purpose of achieving automatic industrial operations in factories without humans in attendance.
In recent years, progress has been made in the research and development of leg-movement-type robots which emulate the movements and mechanisms of the body of an animal, such as a human being or a monkey, which walks on two feet while it is in an erect posture. Therefore, there has been greater expectation for putting such leg-movement-type robots into practical use. A superior feature of leg-movement-type robots which move on two feet while they are in an erect posture is that they can walk flexibly, for example, up and down steps or over obstacles.
In the history of leg-movement-type robots, research regarding leg movement was started by studying as elemental technology leg movement using only the lower limbs. Accordingly, robots of this type are not provided with all parts of the body which are positioned vertically.
For example, Japanese Unexamined Patent Publication No. 3-184782 discloses a joint structure applied to the structural part below the trunk of a robot which walks using the legs.
Japanese Unexamined Patent Publication No. 5-305579 discloses a controller for controlling the walking of a leg-movement-type robot. The controller disclosed in this document controls the walking of the robot so that the ZMP (zero moment point) matches a target value. The ZMP is the point on the floor surface where the moment resulting from the floor reaction force when the robot walks is zero. However, as can be seen from FIG. 1 in this document, a trunk 24 on which the moment acts is formed using a black box, so that not all parts of the body are provided. Therefore, the document is confined to proposing leg movement as elemental technology.
It goes without saying that the ultimate purpose of constructing leg-movement-type robots is to provide these robots with all parts of the body. More specifically, the ultimate purpose is to provide these robots which walk while they are in an erect posture on two feet with the lower limbs used for walking on two feet, the head, the upper limbs (including the arms), and the trunk which connects the upper and lower limbs. In such robots provided with all parts of the body, it is presupposed that work is carried out by moving the two legs while the robots are in an erect posture. In all cases where such work is carried out in the living space of human beings, it is necessary to control the robots so that the upper and lower limbs and the trunk move harmoniously in a predetermined order of priority.
Leg-movement-type robots which emulate the mechanisms and movements of human beings are called humanoid robots. Humanoid robots can, for example, help people in life, that is, help them in various human activities in living environments and in various circumstances in everyday life.
As is conventionally the case, leg-movement-type robots are roughly divided into those for industrial purposes and those for entertainment.
Industrial robots are intended to carry out various difficult operations, such as in industrial tasks or production work, in place of human beings. For example, they carry out in place of human beings maintenance work at nuclear power plants, thermal power plants, or petrochemical plants, or dangerous/difficult work in production plants or tall buildings. The most important theme is to design and manufacture industrial robots so that they can be industrially used as specified and can provide the specified functions. Industrial robots are constructed on the assumption that they walk on two feet. However, as mechanical devices, they do not necessarily have to faithfully reproduce the actual body mechanisms and movements of animals, such as human beings or monkeys, which walk while they are in an erect posture. For example, the freedom of movement of particular parts (such as the finger tips), and their operational functions are increased and enhanced, respectively, in order to produce an industrial robot for a particular use. On the other hand, the freedom of movement of parts considered comparatively unrelated to the use of the industrial robot (such as the head and arms) is limited or such parts are not formed. This causes the industrial robot to have an unnatural external appearance when it works and moves, although it is a type of robot which walks on two feet. However, for convenience in designing such a robot, such a compromise is inevitable.
In contrast, leg-movement-type robots for entertainment provide properties closely connected to life itself, rather than help people in life such as by doing difficult work in place of human beings. In other words, the ultimate purpose of producing robots for entertainment is to make these robots faithfully reproduce the actual mechanisms of, for example, human beings or monkeys, which walk on two feet while they are in an erect posture, and to make them move naturally and smoothly. Since entertainment robots are structured to emulate highly intelligent animals, such as human being or monkeys, which stand in an upright posture, it is desirable that they move in a way sufficiently indicative of emotions and feelings. In this sense, entertainment robots which emulate the movements of human beings are rightly called humanoid robots.
In short, it is no exaggeration to say that entertainment robots, though intently called a leg-movement-type robot, shares the elemental technologies of industrial robots, but are produced for a completely different ultimate purpose and uses completely different hardware mechanisms and operation controlling methods to achieve the ultimate purpose.
As is already well known in the related art, the human body has a few hundred joints, so that it has a few hundred degrees of freedom. In order to make the movements of leg-movement-type robots as close to those of human beings, it is preferable that the leg-movement-type robots be allowed to move virtually as freely as human beings. However, this is technologically very difficult to achieve. This is because, since one actuator needs to be disposed to provide one degree of freedom, a few hundred actuators needs to be disposed for a few hundred degrees of freedom, thereby increasing production costs and making it virtually impossible to design them in terms of, for example, their weight and size. In addition, when the number of degrees of freedom is large, the number of calculations required for, for example, positional/operational control or balance control is correspondingly increased exponentially.
Restating what has been stated in another way, humanoid robots must emulate the mechanisms of the human body equipped with a limited number of degrees of freedom. Entertainment robots are required to move naturally in a way close to that of human beings and in a way sufficiently indicative of emotions and feelings with considerable fewer degrees of freedom than the human body.
Leg-movement-type robots which walk on two feet while they are in an erect posture are excellent robots in that they can walk flexibly (such as up and down steps or over obstacles). However, since the center of gravity of such robots is located at a high position, it becomes correspondingly difficult to perform posture control and stable walking control. In particular, the walking and the posture of entertainment robots need to be controlled while they move naturally and in a way sufficiently indicative of emotions and feelings like intelligent animals, such as human beings or monkeys.
Various proposals regarding the stable walking of leg-movement-type robots have already been made. For example, Japanese Unexamined Patent Publication No. 5-305579 discloses a leg-movement-type robot which is made to walk stably by matching with a target value the zero moment point (ZMP), that is, the point on the floor surface where the moment resulting from the reaction force of the floor when the robot walks is zero.
Japanese Unexamined Patent Publication No. 5-305581 discloses a leg-movement-type robot constructed so that the ZMP is either situated in the inside of a supporting polyhedral (polygonal) member or at a location sufficiently separated by at least a predetermined amount from an end of the supporting polyhedral (polygonal) member when a foot of the robot lands on or separates from the floor. As a result, even when the robot is subjected to an external disturbance, it is not affected thereby in correspondence with a predetermined distance, making it possible make the robot walk more stably.
Japanese Unexamined Patent Publication No. 5-305583 discloses the controlling of the walking speed of a leg-movement-type robot by a ZMP target location. More specifically, in the leg-movement-type robot disclosed in this document, previously set walking pattern data is used to drive an arm joint so that the ZMP matches a target location, and the tilting of the upper part of the body is detected in order to change the ejection speed of the set walking pattern data set in accordance with the detected value. Thus, when the robot unexpectedly steps on an uneven surface and, for example, tilts forward, the original posture of the robot can be recovered by increasing the ejection speed. In addition, since the ZMP can be controlled so as to match the target location, there is no problem in changing the ejection speed in a device for supporting both arms.
Japanese Unexamined Patent Publication No. 5-305585 discloses the controlling of the landing position of a leg-movement-type robot by a ZMP target location. More specifically, the leg-movement-type robot disclosed in this document is made to walk stably by detecting any shifts between the ZMP target location and the actually measured position and driving one or both arms so as to cancel the shift, or by detecting the moment around the ZMP target location and driving an arm so that it becomes zero.
Japanese Unexamined Patent Publication No. 5-305586 discloses the controlling of the tilting of the posture of a leg-movement-type robot by a ZMP target location. More specifically, the leg-movement-type robot disclosed in this document is made to walk stably by detecting the moment around the ZMP target location and driving an arm so that, when the moment is produced, the moment is zero.
However, none of the above-described proposals mention anything about controlling the posture and walking of the robot while it is moving naturally and in a way sufficiently indicative of emotions and feelings like intelligent animals, such as human beings or monkeys.
A robot called WABIAN (Waseda Bipedal Humanoid) is disclosed in a treatise called The Development of Humanoid Robots Which Walk On Two Feet (Third Robotics Symposia, May 7 and 8, 1998) by Yamaguchi et al. WABIAN is a complete humanoid robot which is provided not only with the lower limbs, but also with the upper limbs and the trunk, so that it is provided with all parts of the body. WABIAN has been developed for the purpose of producing a robot whose whole body moves harmoniously while it is walking. FIGS. 13 and 14 are each schematic views of an assembled structure of WABIAN. WABIAN has been designed and manufactured to overcome the problems involved in working while moving the whole body harmoniously. By controlling the ZMP and the yaw axis moment on the ZMP as a result of trunk or trunk/waist harmonious movement three axial moment compensation operations, the robot may be made to walk while its lower limbs, finger tips, and trunk take any path of movement. The mechanical models illustrated in the figures use extra super Duralumin as main structural material, and has a total weight of 107 kg and an overall length of 1.66 m when they are standing still in an erect posture.